Security has been tightened at all Irish airports and sea ports to prevent terror suspects banned or deported from the UK from using Ireland to re-enter Britain.
The move is part of a series of measures implemented by the Irish and British authorities to confront the growing threat posed by jihadis in the EU.
Immigration and security officials have activated a plan which ensures that information about suspects who have been blacklisted in either jurisdiction is shared almost immediately.
This follows the signing of a deal to allow the opening up of a fast-track data-sharing channel.
A total of 350 non-European nationals, including those deemed to be security risks, or the subject of banning orders or career criminals, have been refused permission in the past year to enter the State at the ports by immigration officers.
Those decisions were based on the belief that the suspects intended to travel illegally to the UK. The figure represents an increase of 24pc on the previous year.
Taoiseach Enda Kenny has acknowledged that reports suggesting Ireland was being used as a back door to Europe by jihadis were being monitored carefully.
The agreement was recently signed by Justice Minister Frances Fitzgerald and British Home Secretary Theresa May.
But the measures on data exchange are now in full operation and seal off a loophole that that previously meant information about banned or deported persons was not passed between the two immigration authorities for up to a week.
A senior Justice official told the Irish Independent last night: "This agreement will help prevent people from using one common travel area country as a back door to another, as the data will be available to border officers far quicker than before. The information exchange will apply to both EU and non-EU citizens."
The data-sharing channel applies to those who have been judged to be of risk to the public or are persistent criminal re-offenders while also covering exclusion orders, deportation rulings and deprivation of citizenship.
EU intelligence estimates indicate that up to 80pc of about 2,000 European foreign fighters are aligned with Islamic State in Iraq and the Levant (Isil).
Since the start of the Arab Spring, between 25 and 30 young people have travelled from Ireland to the areas affected. But not all of them have become part of extremist groups such as Isil or al-Qa'ida.
There has also been evidence in the past of terrorist supporters based here providing logistical aid to activists as well as linking into the planning of attacks through the internet.
The latest measure is also intended to underpin the unprecedented level of co-operation between senior Irish and British immigration officials to boost the common travel area, according to Mrs Fitzgerald. Apart from protecting the common travel area from abuse, it also extends the benefits of borderless travel between the two countries to genuine visitors, through initiatives such as the Irish-British visa scheme.
This allows tourists, business people and other eligible travellers to visit the two countries on a single visa.
The tightening up of border checks has been introduced alongside Government moves to clamp down on terrorist financing through new legislation tackling sympathisers of suspect foreign groups.
EU justice ministers, including Ms Fitzgerald, have agreed on a package of short-term measures, which also include improving communications between member states on the movement of suspected fighters, building up case law and jurisprudence experience across the EU in relation to prosecuting those fighters and expanding efforts to combat online radicalisation.